Neuromuscular Control Flashcards
What are alpha motor neurons?
lower motor neurons of the brainstem and the spinal cord
Alpha motor neurons innervate what?
extrafusal muscle fibres of the skeletal muscles
Define a motor unit.
a single motor neuron together with all the muscle fibres that it innervates
Define a motor pool.
contains all alpha motor neurons innervating a single muscle
Describe type I motor units.
slow smallest diameter cell bodies small dendritic trees thinnest axons slowest conduction velocity
Describe type IIA motor units.
fast, fatigue resistant larger diameter cell bodies larger dendritic trees thicker axons faster conduction velocity
Describe type IIB motor units.
fast, fatiguable larger diameter cell bodies larger dendritic trees thicker axons faster conduction velocity
How are the three motor unit types classified?
amount of tension generated
speed of contraction
fatiguability
How is muscle force regulated?
recruitment
rate coding
How are motor units recruited?
size principle - smaller units are recruited first
What is rate coding?
as firing rate of motor units increases, the force produced by the unit increases
What are neurotrophic factors?
a type of growth factor
Prevent neuronal death
Promote growth of neurons after injury
Are motor unit and fibre characteristics are dependent or independent on the nerve which innervates them?
dependent e.g. cross innervation
Type IIB fibres can change to type IIA fibres most commonly by?
training
Type I fibres can change to type II fibres possible by?
severe deconditioning or spinal cord injury
microgravity in space flight
Ageing is associating with what change in muscle fibre?
loss of type I and II fibres but also preferential loss of type II fibre
What is an involved in an automatic response to a stimulus?
a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness (REFLEX)
Reflexes vs voluntary movements
once reflexes they are released, they can’t be stopped vice versa for voluntary
What is the Jendarssik manouvre?
clenching the teeth, making a fist, or pulling against locked fingers when having patellar tendon tapped > reflex becomes larger
What control dominates on stretch reflex?
inhibitory
What process reveals the excitatory control from supraspinal areas?
decerebration (the elimination of cerebral brain function by removing the cerebrum)
What can result from brain damage giving over active or tonic stretch reflex?
rigidity
spasticity
What is hyperreflexia?
overactive reflexes, loss of descending inhibition
Is hyperreflexia associated with upper or lower motor neuron lesions?
upper motor neurons
What is clonus?
Involuntary and rhythmic muscle contractions, loss of descending inhibition
Is clonus associated with upper or lower motor neuron lesion?
upper motor neurons lesions
What is the Babinski sign? Include +ve and -ve results.
sole stimulated with blunt instrument > -ve results big toe curls downward, +ve result big toe curls upward (abnormal in adults)
What is hyporeflexia?
below normal or absent reflexes
Hyporeflexia is associated with upper or lower motor neuron lesions?
lower motor neuron lesion
